21102021 has 12 divisors (see below), whose sum is σ = 30659148. Its totient is φ = 13985664.

The previous prime is 21101963. The next prime is 21102023. The reversal of 21102021 is 12020112.

It can be written as a sum of positive squares in 2 ways, for example, as 17969121 + 3132900 = 4239^2 + 1770^2 .

It is not a de Polignac number, because 21102021 - 2¹¹ = 21099973 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a junction number, because it is equal to n+sod(n) for n = 21101994 and 21102012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21102023) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5220 + ... + 8333.

It is an arithmetic number, because the mean of its divisors is an integer number (2554929).

Almost surely, 2^21102021 is an apocalyptic number.

It is an amenable number.

21102021 is a deficient number, since it is larger than the sum of its proper divisors (9557127).

21102021 is a wasteful number, since it uses less digits than its factorization.

21102021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13732 (or 13729 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 9.

The square root of 21102021 is about 4593.6936118988. The cubic root of 21102021 is about 276.3384710117.

Adding to 21102021 its reverse (12020112), we get a palindrome (33122133).

The spelling of 21102021 in words is "twenty-one million, one hundred two thousand, twenty-one".